Bronchodilating properties of the VIP receptor agonist Ro 25-1553 compared to those of formoterol on the guinea-pig isolated trachea.

Ro 25-1553 is a 31-amino acid analogue of vasoactive intestinal peptide (VIP) and has recently been shown to be highly selective for the VPAC(2)-receptor. The bronchodilating property of this compound was evaluated in vitro on preparations of guinea-pig trachea, with the long-acting beta(2)-adrenoceptor selective agonist, formoterol, as a reference. In strip-preparations precontracted with carbachol, Ro 25-1553 caused a concentration-dependent and complete relaxation of the tracheal smooth muscle. Ro 25-1553 was 3-7 times less potent than formoterol on a molar basis, but the efficacy was comparable with that of formoterol. Both compounds showed a rapid onset of action and a similar durability of effect. Ro 25-1553 appeared to interact with formoterol as well as with salmeterol in an additive way. In vagus nerve-trachea tube preparations, when added to the external medium, Ro 25-1553 concentration-dependently and completely inhibited nerve-induced contractions. This occurred in the same concentration range as needed for relaxation of precontracted strips. Ro 25-1553 was active also when administered into the tracheal lumen albeit the concentration had to be increased. The present study supports and extends previous results suggesting that Ro 25-1553 may be a powerful alternative to the beta(2)-adrenoceptor agonists which prevail today.

The effect of the enantiomers of formoterol on inherent and induced tone in guinea-pig trachea and human bronchus.

The long-acting beta2-adrenoceptor agonist formoterol is, like all other members of this class of drugs, used as a racemate in the clinic. While the effects of the individual enantiomers have been studied on airway smooth muscle from guinea pig, comparable data on human bronchial smooth muscle are scanty or absent. Therefore, we compared the effects of the enantiomers of formoterol on inherent and induced tone in isolated human bronchi with that on guinea-pig trachea in vitro. The human bronchi either were studied under resting tension conditions or were precontracted with 10 microM carbachol or 0.1 mM histamine. The guinea-pig trachea was precontracted with 0.01, 0.1 or 1 microM carbachol. The racemate and (R,R)-formoterol caused a concentration-dependent relaxation of all preparations with an EC50 of about 1 nM. In the guinea-pig trachea, the concentration-effect curve for formoterol was moved to the right in response to an increased concentration of carbachol. In both human bronchus and guinea-pig trachea, (S,S)-formoterol was more than 1,000 times less potent than (R,R)-formoterol. Thus the relaxing effect of formoterol in human airways as well as in guinea-pig trachea was shown to lie with the (R,R)-enantiomer. Notably, (S,S)-formoterol did not exert any contractile effects within the tested concentration range in either airway preparation. Therefore, we conclude that with regard to relaxant effects the pure (R,R)-enantiomer of formoterol does not offer a benefit over the racemate.

Steric aspects of formoterol and terbutaline: is there an adverse effect of the distomer on airway smooth muscle function?

Experiments were made on isolated tissues from guinea-pig to test the hypothesis that the distomers of rac-beta 2-adrenoceptor agonists induce airway hyperreactivity. Tracheal strip preparations were contracted with carbachol. Both rac- and (R;R)-formoterol (2 and 1 mumol/l, respectively) produced an immediate relaxation, followed by a slow recovery of tone. (S;S)-Formoterol (2 mumol/l) had no effect on smooth muscle tone. Similar results were obtained with the enantiomers of terbutaline. In other strip preparations of the trachea or the main bronchi, cholinergic or nonadrenergic/noncholinergic (NANC) excitatory responses were evoked by electrical field-stimulation. The eutomers, (R;R)-formoterol and (R)-terbutaline, inhibited concentration-dependently both cholinergic and NANC-induced contractions. The distomers, (S;S)-formoterol and (S)-terbutaline, showed qualitatively the same effects but were about 1,000 times less potent than the corresponding eutomer. In a third series of experiments, either enantiomer of formoterol was administered to an electrically stimulated vagus nerve-trachea tube preparation. The nerve-induced contractions were inhibited by both enantiomers, but (S;S)-formoterol was about 1,000 times less potent than (R;R)-formoterol. For both enantiomers of formoterol, about tenfold higher concentrations was required to obtain the same degree of inhibition when given intratracheally as compared with administration in the external medium. There was no indication in any of the experimental approaches that (S;S)-formoterol or (S)-terbutaline might enhance the response to cholinergic or NANC-related stimuli.

The interaction between salmeterol and beta 2-adrenoceptor agonists with higher efficacy on guinea-pig trachea and human bronchus in vitro.

1. In guinea-pig tracheal preparations precontracted with 1 mumol l-1 carbachol, formoterol, procaterol, fenoterol, salmefamol, salbutamol and terbutaline (in that order of potency) caused a concentration-dependent and almost complete, relaxation. However, under these conditions, the maximum relaxation by salmeterol was approximately 30% of the maximum attainable relaxation. 2. We have therefore explored the ability of salmeterol to inhibit the relaxant response to beta 2-adrenoceptor agonists of different chemical structure and relatively higher efficacy in smooth muscle preparations from guinea-pig trachea and human bronchus. 3. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curves for the other agonists were shifted to the right in a variable way by 1.8-2.8 log units, fenoterol and salbutamol being the extremes. 4. When 20 mumol l-1 sulfonterol, another low efficacy beta 2-adrenoceptor agonist, was substituted for salmeterol, the difference in the magnitude of the rightward shift between fenoterol and salbutamol was eliminated. 5. In the human bronchus, formoterol and terbutaline had a higher apparent efficacy than salmeterol. With 1 mumol l-1 salmeterol in the organ bath, the concentration-effect curve for formoterol was shifted 2.7 log units to the right. 6. Salmeterol inhibits, competitively, relaxant responses to beta 2-adrenoceptor agonists with higher efficacy. The degree of inhibition seems to be dependent on the agonist used. This contrasts with results obtained with sulfonterol and suggests that salmeterol interacts with the beta 2-adrenoceptor in a complex way.

Studies on the interaction between formoterol and salmeterol in guinea-pig trachea in vitro.

The actions of and interaction between formoterol and salmeterol were studied on guinea-pig trachea in vitro. Tracheal strip preparations were contracted by 1 mumol/l carbachol giving a near maximal contraction. Salmeterol in concentrations from 0.1 to 3 mumol/l relaxed the tracheal smooth muscle by about 30 per cent of the maximum relaxation produced by theophylline. Formoterol caused a concentration-dependent and almost complete relaxation with a pD2 of 8.56. In the presence of salmeterol there was a rightward shift of the concentration-response curve for formoterol. The pA2 for salmeterol was estimated to 7.42. Similar experiments with isoprenaline indicated that salmeterol has a low affinity for beta 1-adrenoceptors. Formoterol and salmeterol both inhibited in a concentration-dependent manner the contractions evoked by stimulation of the vagus nerve in a tracheal tube preparation. The degree of inhibition decreased with increasing stimulation frequency. Complete inhibition was attained with salmeterol, but not with formoterol, at the highest frequency employed (45 Hz). The inhibiting effect of 10 mumol/l salmeterol was not blocked by 10 mumol/l sotalol, a beta-adrenoceptor antagonist. It is concluded that salmeterol, in comparison to formoterol, is a partial beta 2-adrenoceptor agonist and has, at high concentrations, an additional unspecific inhibitory action.

Steric aspects of agonism and antagonism at beta-adrenoceptors: synthesis of and pharmacological experiments with the enantiomers of formoterol and their diastereomers.

The enantiomers of formoterol (R;R and S;S) and their diastereomers (R;S and S;R) were synthesized and purified using a new procedure which required the preparation of the (R;R)- and (S;S)-forms of N-(1-phenylethyl)-N-(1-(p-methoxyphenyl)-2-propyl)-amine as important intermediates. The enantiomeric purity obtained was greater than 99.3%, usually greater than 99.7%. The four stereoisomers were examined with respect to their ability to interact in vitro with beta-adrenoceptors in tissues isolated from guinea pig. The effects measured were (1) relaxation of the tracheal smooth muscle (mostly beta 2), (2) depression of subtetanic contractions of the soleus muscle (beta 2), and (3) increase in the force of the papillary muscle of the left ventricle of the heart (beta 1). All enantiomers caused a concentration-dependent and complete relaxation of the tracheal smooth muscle which was inhibited by propranolol. The order of potency was (R;R) much greater than (R;S) = (S;R) greater than (S;S). There was a 1,000-fold difference in potency between the most and the least potent isomer. The presence of the (S;S)-isomer did not affect the activity of the (R;R)-isomer on the tracheal smooth muscle. Also on the skeletal and cardiac muscles (R;R)-formoterol was more potent than its (R;S)-isomer. The selectivity for beta 2-adrenoceptors appeared to be slightly higher for the (R;R)-isomer than for the (R;S)-isomer. The potency of the (S;R)- and (S;S)-isomers on the papillary muscle was too low to be determined accurately.(ABSTRACT TRUNCATED AT 250 WORDS)